Reduction of Stormwater Runoff Toxicity by Wet Detention Ponds - Highway and Urban Environment - page 157

Reduction of Stormwater Runoff Toxicity
by Wet Detention Ponds
Tove Wium-Andersen, Asbjørn H. Nielsen, Thorkild Hvitved-Jacobsen,
and Jes Vollertsen
Introduction
Stormwater runoff contains a wide range of contaminants [1] . Pollutants like
PAH's, biocides, heavy metals and nutrients are often found in varying, but signifi-
cant concentrations. Due to the content of various contaminants, stormwater runoff
has been found to be toxic to the aquatic environment [2-4] , with potential negative
ecological impacts on receiving waters.
Toxic effects are estimated by exposing test organisms to the potential toxic
sample or compound followed by a calculation of the inhibition of the test organ-
ism. The inhibition can be growth inhibition, mobility inhibition, inhibition of the
reproduction and etceteras. Inhibition is expressed as a given effect concentration
(EC) after a given exposure time. That is, EC50 is the concentration giving an inhi-
bition equal to 50% after a certain exposure time and EC10 is the concentration
giving an inhibition equal to 10% after a certain exposure time. Toxicity is not an
absolute estimation but a relative measurement characteristic for the test organism
applied, resulting in different EC50 values for the same compound. Therefore, it is
important to consider which organisms that is relevant to use as test organisms for
environmental samples such as stormwater runoff. The optimal solution is to use a
battery of toxicity tests to reveal the ecological impacts of a sample [5] .
To reduce the content of nutrients, organic matter and the different organic and
inorganic micro pollutants, the stormwater runoff can be led through a wet deten-
tion pond where sedimentation and uptake by plants reduce the concentration of the
contaminants. To improve sedimentation, a flocculent such as aluminum can be
added to the water phase. It is well known that aluminum can reduce the content of
phosphorous in the water phase in lakes [6] , but whether aluminum addition also
reduces the toxic effect of the water phase has not been identified.
T. Wium-Andersen, A.H. Nielsen, T. Hvitved-Jacobsen, and J. Vollertsen
Aalborg University, Section of Environmental Engineering, Sohngaardsholmsvej 57, 9000,
Aalborg, Denmark